Returns pixel format of an image: Bits per pixel, Alpha channels, RGB, Grayscale, Indexed etc
#include <GDIPlus.au3>
_GDIPlus_ImageGetPixelFormat ( $hImage )
| $hImage | Handle to an image object | 
| Success: | an array with the following format: [0] - Integer of pixel format constant [1] - String of pixel format | 
| Failure: | sets the @error flag to non-zero, @extended may contain GPSTATUS error code ($GDIP_ERR* see GPIPlusConstants.au3). | 
| @error: | 10 - Invalid pixel format. 11 - Invalid image handle. 12 - Unknown pixel format. | 
_GDIPlus_BitmapCloneArea, _GDIPlus_BitmapLockBits, _GDIPlus_ImageGetFlags
Search GdipGetImagePixelFormat in MSDN Library.
#include "Extras\HelpFileInternals.au3"
#include <GDIPlus.au3>
#include <GUIConstantsEx.au3>
#include <ScreenCapture.au3>
#include <WinAPIHObj.au3>
#include <WindowsStylesConstants.au3>
Example()
Func Example()
    Local $hBitmap, $hImage, $aRet
    ; Create GUI
    GUICreate("GDI+", 600, 400)
    _MemoCreate(2, 2, 596, 396, $WS_VSCROLL)
    GUISetState(@SW_SHOW)
    ; Initialize GDI+ library
    _GDIPlus_Startup()
    ; Capture 32 bit bitmap
    $hBitmap = _ScreenCapture_Capture("")
    $hImage = _GDIPlus_BitmapCreateFromHBITMAP($hBitmap)
    ; Show pixel format for screen capture
    $aRet = _GDIPlus_ImageGetPixelFormat($hImage)
    _MemoWrite("Image pixel format of screen capture: " & $aRet[1]) ;
    _MemoWrite("Image pixel format constant: " & $aRet[0]) ;
    _MemoWrite() ;
    ; Save screen capture bitmap to file
    _GDIPlus_ImageSaveToFile($hImage, @MyDocumentsDir & "\GDIPlus_Image.jpg")
    ; Clean up resources
    _GDIPlus_ImageDispose($hImage)
    _WinAPI_DeleteObject($hBitmap)
    ; Load screen capture bitmap from file
    $hImage = _GDIPlus_ImageLoadFromFile(@MyDocumentsDir & "\GDIPlus_Image.jpg")
    ; Show pixel format for saved file
    $aRet = _GDIPlus_ImageGetPixelFormat($hImage)
    _MemoWrite("Image pixel format of saved file: " & $aRet[1]) ;
    _MemoWrite("Image pixel format constant: " & $aRet[0]) ;
    ; Clean up resources
    _GDIPlus_ImageDispose($hImage)
    ; Shut down GDI+ library
    _GDIPlus_Shutdown()
    ; Loop until the user exits.
    Do
    Until GUIGetMsg() = $GUI_EVENT_CLOSE
EndFunc   ;==>Example